Fluid-operated braking systems such as air brake systems have long been used to control the movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel requires a braking system which responds rapidly with substantial braking power. One system component which is instrumental in the operation of air brake systems is the brake actuator. The brake actuator provides the force necessary when braking a vehicle. The assignee of the present invention produces a number of high-quality commercial air brake actuators, many of which actuate the normal service brakes as well as parking/emergency brakes. These brake actuators, also known as spring brakes, typically have a network of air chambers defined by one or more diaphragms or pistons and a plurality of springs which operate to provide the appropriate braking action in response to directives by the vehicle driver. In the event an air braking system loses pressure, the brake actuator automatically engages the vehicle brakes.
Brake actuators of this type, with or without a service brake section, have a powerful coil spring seated within a housing or head portion of the actuator. When compressed, the power spring exerts a biasing force in an axial direction relative to the housing. The power spring has a high spring constant such that, once compressed, it has a substantial amount of potential energy. When released, the stored energy of the spring is converted into kinetic energy to be used in the braking operation. However, premature removal of the actuator head, that is, removal of the head while the power spring is compressed, may cause this energy to be released in an undesirable manner. For example, the actuator cap or head assembly is typically attached to the flange case using a single or multiple section ring clamp, the clamp being secured in position by one or more retaining bolts. In the field, the injudicious removal of these retaining bolts may release the ring clamp causing the head or cap to detach from the case flange. Once released, the immense energy of the spring is transmitted to the actuator head which is propelled away from the flange case with considerable force. Hence, the air pressure which retains the power spring in its compressed state must be dissipated prior to the removal of the clamp, and the power spring must be "caged" within the head. Moreover, these prior art clamp rings can be difficult to position when assembling the actuator.
Typically, instructions are attached to the brake actuators to inform those attempting inspection or repair of the presence of the power spring and of the consequences which may result from tampering with the head retaining ring clamp when the power spring is in the compressed state, evidencing recognition by the art of the tampering problem. However, it would still be desirable to provide a device for attaching the actuator head to the flange case in a manner which would prevent removal in the field.
Restraining and clamping devices have been proposed by others for addressing the improvident detachment of a brake actuator head from the flange case. In U.S. Pat. No. 4,565,120, a device for restraining the separation of brake actuator housings is disclosed which consists of a sheet metal body having a notch which receives the housing flanges. The notch is large enough to permit partial separation of the housing flanges upon release of the flange clamp band. A number of clamping bands are also known such as those disclosed in U.S. Pat. Nos. 3,106,757, CLAMP STRUCTURE FOR METAL BANDS, 3,295,176, HOSE CLAMPS, 4,583,773, RELEASABLE TUBULAR CLAMPS FOR THE CONNECTION OF CYLINDRICAL OR PROFILED TUBES, 4,451,955, CRIMP-TYPE CLAMP, 4,430,775, MUFFLER SHIELD BANDING STRAP, 3,602,954, ANNULAR HOSE CLIP, 2,541,205, and 4,109,305, CLAMP BAND. For a variety of reasons, none of these latter clamping devices, however, are appropriate for providing a tamper-resistant brake actuator, nor is any such use disclosed or suggested by these references which are considered to be nonanalogous art with respect to brake actuators. Thus, to meet this need, the present invention provides a reliable tamper-resistant fluid-operated brake actuator.